1. Field of the Invention
Exemplary embodiments of the present invention relate to a method and an apparatus for decoding a speech signalT and more particularly, to a method and an apparatus for decoding a speech signal using adaptive codebook update.
2. Description of Related Art
The encoder and decoder are required for a speech(audio) communication. The encoder compresses a digital speech signal and the decoder reconstructs a speech signal from the encoded frame data. One of the most widely used speech coding (encoder and decoder) technologies is the code excited linear prediction (CELP). The CELP codec represents the speech signal with a synthesis filter and an excitation signal of that filter.
A representative example of the CELP codec may include a G.729 codec and an adaptive multi-rate (AMR) codec. Encoders of these codecs extract synthesis filter coefficients from an input signal of one frame corresponding to 10 or 20 msec and then divide the frame into several subframes of 5 msec. And it obtains pitch index and gain of the adaptive codebook and pulse index and gain of the fixed codebook in each subframe. The decoder generates an excitation signal using the pitch index and gain of the adaptive codebook and the pulse index and gain of the fixed codebook and filters this excitation signal using the synthesis filter, thereby reconstructing speech signal.
A frame data loss may occurs according to the condition of communication network during the transmission of the frame data which is an output of the encoder. In order to reduce a quality degradation of the decoded signal of the lost frame, a frame loss concealment algorithm is required. Most of the frame loss concealment algorithms recover the signal of the lost frame by using a normal frame data which received without loss just before the frame data loss. However, the quality of the normally decoded frame just after the frame data loss is also effected by the influence of the lost frame. And the frame data loss causes quality degradation of the normal frame as well as lost frame. Therefore, not only the frame loss concealment algorithm for a lost frame but also fast recovering algorithm for a normal frame received just after the frame loss is required.